lawyer for the Archdiocese of Boston yesterday asked a judge to dismiss nearly 500 civil lawsuits filed by alleged victims of clergy abuse, arguing that secular courts cannot legally plumb the relationship between church leaders and their priests.

The archdiocese brought in a Colorado lawyer and First Amendment expert to make its case yesterday before Judge Constance M. Sweeney in Suffolk Superior Court.

L. Martin Nussbaum argued that the relationship between church officials and priests - involving issues of church doctrine, sacramental practices, and canon law - is much different from the relationship between a secular employer and employee.

''It is absolutely our position that when it comes to this bishop-priest relationship ... the court can't get into the business of defining what a reasonably prudent bishop would do in that relationship,'' said Nussbaum, who attached Bible passages and writings of St. Augustine to his legal brief.

Sweeney repeatedly interrupted Nussbaum to question him about his argument, proposing hypothetical examples and then asking for his response. She described the case of a bishop who knew a priest was raping children, yet kept reassigning him to new parishes, suggesting that there would be ''at least a serious issue'' of criminally charging the bishop as an accessory after the fact.

Nussbaum declined to answer her question, saying he wasn't familiar with Massachusetts criminal law. He gave a similar answer when Sweeney asked him whether his argument would gut the state's new mandatory reporting requirement for clergy who learn about possible child abuse.

Sweeney, who said she will rule in about a month, also questioned Nussbaum about the breadth of his argument.

''It appears to me the [archdiocese] is taking the position that they have absolute immunity on all civil court actions,'' Sweeney said.

Nussbaum disagreed. He said church officials wouldn't fight criminal prosecution of offending priests, or civil lawsuits filed against the priests themselves, if not their supervisors. Alleged victims can also turn to the church's ecclesiastical courts, he said.

The alleged victims argue in their lawsuits that church leaders were negligent in overseeing pedophile priests, shuffling them from parish to parish, even as they knew the priests would probably continue to molest children.

Yesterday, lawyers for the alleged victims asked Sweeney not to dismiss the lawsuits, arguing that while the First Amendment protects religious belief, it doesn't protect illegal conduct. The church is using the Constitution to evade its responsibility for returning pedophile priests to parishes, the lawyers said.

''This Catholic Church does not want us to use our law to decide these cases,'' said Jeffrey Newman, one of the lawyers. ''It wants to use their own internal law.''

Another lawyer for alleged victims, William H. Gordon, argued that the church tried to cover up, rather than prevent, sexual abuse by priests.

Lawyers for the alleged victims have argued that other states have rejected arguments like Nussbaum's. Once before, Sweeney rejected the First Amendment argument when she allowed the Globe's motion in November 2001 to unseal church records in the case of defrocked priest John J. Geoghan.

When the archdiocese filed its motion to dismiss the civil lawsuits, archdiocesan officials said the legal argument was necessary to satisfy the church's insurance carriers that the archdiocese was vigorously fighting the lawsuits.

After the hearing yesterday, a spokesman for the archdiocese declined to discuss the legal issues. Reading from a prepared statement, the spokesman said the church remains committed to reaching a ''global resolution'' of the legal claims.

''We reiterate that today's motion in no way seeks to diminish the serious nature of what has been experienced by victims in this archdiocese,'' said the Rev. Christopher J. Coyne. ''However, we have a responsibility to protect our unique constitutional inheritance of the separation of church and state.''

In court, Nussbaum said that the church believes that people can genuinely change. ''Some of the greatest leaders in church history are, as the church would say, redeemed sinners, but as our civil justice might say, former criminals,'' he said.